Every year, the YMCA/City Pool in Twin Falls goes through a transformation of sorts.

In May, an air-supported bubble that shelters the pool in wintertime comes down, giving swimmers summertime sunlight. And then in September, it goes back up, keeping the wintertime chills away.

In a few years — probably 2015 or even later — the bubble will reach the end of its lifespan. While that’s still six years or more down the road, city officials are already starting to look ahead and plan for the long-term future.

The choices vary, and nothing has been decided for sure. One option is setting aside $50,000 a year in the city budget so there’s money saved up when the bubble’s replacement is needed, said Dennis Bowyer, parks and recreation director.

It would cost about $250,000 for a new bubble’s fabric, blower unit and new emergency doors, he said.

“Trying to come up with that in one year would be quite expensive,” Bowyer said.

If the city starts saving $50,000 a year in the next fiscal year, which starts in October 2010, there will be $250,000 available by 2015, he said.

By then, the bubble would be 16 years old. When the bubble was added to the pool in 1999, the city was told that it would last 15 to 18 years if properly cared for, Bowyer said.

“Maybe it will last a couple years after that — we just don’t know,” Bowyer said.

The idea of building a retractable dome has been raised, according to meeting minutes, but Bowyer stressed that no research into that prospect has taken place.

“We have talked about do we try to put a permanent structure over that,” he said, adding that all discussions by the pool advisory commission are in early stages. “ … Maybe we should look at that too.”

Produced by Yeadon, a Canadian company, the bubble is a high-strength polyester fabric that comes in three sections that are bolted together.

Each section weighs 5,000 pounds.

It came with a 10-year warranty, and there have been small rips that have been fixed, Bowyer said.

While the bubble keeps out sunlight, that didn’t seem to dampen the enthusiasm of swimmers participating in water aerobics on Friday — who prefer the bubble and warmth to not being able to swim throughout the year.

“If they didn’t have the bubble, I wouldn’t come,” said Theresa Cotroneo of Twin Falls. “For me, this is my second home.”

The city owns the pool and has an management agreement with the YMCA of Twin Falls.

Ben Botkin may be reached at bbotkin@magicvalley.com or 208-735-3238.